1. Field of the Invention
The present invention relates to a semiconductor integrated circuit device, an electric circuit device, electronic equipment, and control equipment in which countermeasures against EMI (electromagnetic interference) are taken. More specifically, the present invention relates to a semiconductor integrated circuit device, an electric circuit device, electronic equipment, and control equipment for preventing EMI caused by switching noise generated in the power circuit of a die.
2. Background
Simultaneous with the increase in the internal operating frequency and power consumption of semiconductor integrated circuit devices, EMI caused by the switching noise of the internal power circuit in semiconductor integrated circuit devices has raised serious problems. The switching noise current of the internal power circuit in semiconductor integrated circuit generates a loop current in an IC package, and a loop current circulating through the IC package and the PCB (printed circuit board) outside the IC package. These loop currents generate electromagnetic fields that radiate from the IC package and the PCB causing EMI in the surrounding environment.
One of the conventional countermeasures against the EMI of semiconductor integrated circuit devices is to place a decoupling capacitor between the power line and the ground line of the PCB. Although this conventional countermeasure can inhibit the radiation of electromagnetic fields from the PCB, it is difficult to inhibit the radiation of electromagnetic fields from the semiconductor integrated circuit device itself. Also, in order to prevent EMI caused by the entire PCB on which a large number of semiconductor integrated circuit devices are mounted, decoupling capacitors must be provided on the PCB to correspond to each power lead of each semiconductor integrated circuit device. As the number of decoupling capacitors on the entire PCB increases, problems arise such as increasing the size of the PCB, increasing the number of components on the PBC, and difficulty in finding locations to install decoupling capacitors on the PCB. Also, there is a case where an island-shaped ground plane is formed on the surface of a PCB that is covered with semiconductor integrated circuit devices in order to shield the electromagnetic fields radiated from the semiconductor integrated circuit devices. It is difficult, in this case, to form various wirings on the ground plane.
Japanese Published Unexamined Patent Application No. 4-277665 discloses a socket used for the tester of semiconductor integrated circuit devices. This socket comprises a contact fixed on the testing board for contacting and pressing the leads of semiconductor integrated circuit devices, an electrical conductor disposed so as to contact the ground pattern on the surface of the testing board, and a decoupling capacitor intervening between the contact and the electrical conductor. However, this structure is applied to the socket of a semiconductor integrated circuit device, and does not act to inhibit the switching noise current that is output from the semiconductor integrated circuit device. Also in this socket, since the electrical conductor contacts the ground pattern on the surface of the testing board two-dimensionally, and the impedance between the decoupling capacitor and the testing board is substantially lower than the impedance between the decoupling capacitor and the semiconductor integrated circuit device, the socket cannot inhibit the flow of the switching noise current leaked from the semiconductor integrated circuit device to the testing board.
In the semiconductor integrated circuit device disclosed in Japanese Published Unexamined Patent Application No. 8-17960, the bottom of the semiconductor integrated circuit device is formed of a ground plane, or from a central mounting plate and a circumferential power supply frame, and the ground plate and the power supply frame substitute for ground leads and power leads, thereby decreasing the number of leads on the side of the semiconductor integrated circuit device. Furthermore, in FIG. 4(b) of Japanese Published Unexamined Patent Application No. 8-17960, a power supply plane facing the ground plane is provided in the package of the semiconductor integrated circuit device, so that the power supply plane and the ground plane constitute a decoupling capacitor. In this semiconductor integrated circuit device, however, the ground plate and the power supply frame are directly and two-dimensionally in contact with the ground line and the power line of the PCB, and as a result, the impedance between the ground plane and the power supply frame, and the PCB is substantially lower than the impedance between the ground plane and the power supply frame, and the die. Further, the leakage of the noise current to the PCB cannot be sufficiently inhibited. In this semiconductor integrated circuit device, since the ground plane is used both as the path of the switching noise current returned from the die through the decoupling capacitor to the die in the package, and as the path of the return current of the transmission signal, ground-bound noise generated by the inductance of the ground plane cannot be inhibited. Furthermore, in this semiconductor integrated circuit device, since the center of the ground plane is protruded and the die is disposed on the protruded surface, problems such as an increase in capacitance of the internal circuit of the IC package, and degradation of the quality of the signal transmission in the die may occur.
An object of the present invention is to provide a semiconductor integrated circuit device that can effectively inhibit EMI caused by a loop current circulating between the package and the printed circuit board for mounting electronic parts caused by the switching noise current of the internal power supply circuit in the semiconductor integrated circuit device.
Another object of the present invention is to provide a semiconductor integrated circuit device that can effectively inhibit EMI caused by a loop current in the package caused by the switching noise current of the internal power supply circuit in the semiconductor integrated circuit device.
Another object of the present invention is to provide a semiconductor integrated circuit device that does not require forming an island-shaped ground plane on the printed circuit board for mounting electronic parts for shielding the printed circuit board from the electromagnetic fields radiated by the semiconductor integrated circuit device.
Another object of the present invention is to provide an electric circuit device that can effectively inhibit EMI caused by semiconductor integrated circuit devices, and the printed circuit board for mounting electronic parts.
Another object of the present invention is to provide electronic equipment and control equipment furnished with semiconductor integrated circuit devices, and can effectively inhibit EMI.
A semiconductor integrated circuit device according to a first aspect of the present invention comprises:
a die connected to a ground lead and a power lead,
a ground plane extending two-dimensionally and connected to the ground lead,
a decoupling capacitor connected to the ground lead at one end and to the power lead at another end, and
an encapsulating material for encapsulating the die, ground plane, and decoupling capacitor.
When the surfaces of a semiconductor integrated circuit device facing the printed circuit board for mounting electronic parts and facing opposite to the printed circuit board for mounting electronic parts are defined as the bottom surface and the top surface, respectively, the ground plane is typically parallel to the top and bottom surfaces of the encapsulating material, but is not necessarily parallel The ground plane is preferably perpendicular to the direction in which the inhibition of electromagnetic radiation from the semiconductor integrated circuit device is desired. The ground plane is not limited to be flat, but may be curved, such as convex or concave toward the die. Although the number of the ground planes in a semiconductor integrated circuit device is typically one, when the semiconductor integrated circuit device has a plurality of power leads, multiple ground planes may be adequately dispersed depending on the distribution of power leads in the semiconductor integrated circuit device. When a semiconductor integrated circuit device has multiple ground planes, these ground planes may be in contact with each other, or they may be apart from each other and connected to the ground lead.
When a semiconductor integrated circuit device has multiple power leads, decoupling capacitors are not necessarily provided to all the power leads. The decoupling capacitors can be provided to specific power leads among all the power leads. When the decoupling capacitors are not provided to all the power leads, the decoupling capacitors can be provided to only the power leads of which switching noise voltages or currents are high. For example, when the semiconductor integrated circuit device is a CPU, it is preferable to provide decoupling capacitors focusing on the power leads of high-speed operation circuits (e.g., the CPU core, the PLL circuits, and the output buffer).
The capacitance of the decoupling capacitor is determined according to the frequency of switching noise voltages or currents generated in the power circuit of the die, and is in a range between several tens of pF and several Î{fraction (1/4)} F. The frequency of electromagnetic fields that can most effectively inhibit EMI by allowing a decoupling capacitor to intervene between the ground plane and the power lead relates to the capacitance of the decoupling capacitor, as well as the inductance of the power lead. Therefore, the effect of inhibiting EMI can be improved by matching the capacitance of the decoupling capacitor and the inductance of the power lead to the frequency of switching noise voltages or currents generated in the power circuit.
The ground lead and the power lead act as a certain inductance against switching noise voltages generated in the power circuit of the semiconductor integrated circuit device. Therefore switching noise currents generated in the power circuit of the semiconductor integrated circuit device flow preferentially through the decoupling capacitor, the leakage of the switching noise currents to the printed circuit board for mounting electronic parts through the ground lead and the power lead is inhibited, and EMI from the wiring substrate for mounting is prevented. Also, the ground plane extending two-dimensionally shields electromagnetic fields radiated from the die, thereby attenuating the electromagnetic fields outwardly radiated from the semiconductor integrated circuit device.
According to the semiconductor integrated circuit device of a second aspect of the present invention, in the semiconductor integrated circuit device according to the first aspect of the present invention, the plane facing a printed circuit board for mounting electronic parts, and the plane facing opposite to the printed circuit board for mounting electronic parts, are defined as the bottom surface and the top surface, respectively; and the ground planes extend along the bottom surface.
When the package is a QFP (quad-flat package) or a DIP (dual inline package), the top surface and the bottom surface of the semiconductor integrated circuit device coincide with the top surface and the bottom surface of the mold. When the package is of a BGA (ball grid array) type, since a carrier PCB is further disposed on the bottom surface, the top surface of the semiconductor integrated circuit device coincides with the top surface of the mold, but the bottom surface of the semiconductor integrated circuit device coincides with the bottom surface of the carrier PCB.
Since the ground plane extends along the bottom surface of the semiconductor integrated circuit device, electromagnetic fields to be radiated from the semiconductor integrated circuit device toward the printed circuit board caused by the switching noise current is shielded by the ground plane, and EMI from the semiconductor integrated circuit device to the printed circuit board for mounting electronic parts is inhibited. Therefore, even if signal wirings are formed in the area of the printed circuit board for mounting electronic parts immediately underneath the semiconductor integrated circuit device, the adverse effect of the wirings on signals can be prevented.
According to the semiconductor integrated circuit device of a third aspect of the present invention, the ground planes extend two-dimensionally substantially throughout the bottom surface of the semiconductor integrated circuit device of the second aspect of the present invention.
When the package is a semiconductor integrated circuit device of, for example, a QFP or a DIP, the ground plane may be a plane without holes; however, when the package is a semiconductor integrated circuit device of, for example, a BGA, the lead must be passed through the ground plane. Therefore, holes for passing the lead are formed in the ground plane. The ground plane is extending in two dimensions over substantially the entire bottom surface of the semiconductor integrated circuit device which effectively prevents electromagnetic radiation at the bottom surface.
According to the semiconductor integrated circuit device of a fourth aspect of the present invention, an intra-package wiring substrate comprising wirings for the connecting path between leads and the bonding pads of the die is disposed between the die and the ground plane, and the decoupling capacitor is connected to the ground plane and the power line of the intra-package wiring substrate at either end in the semiconductor integrated circuit device of the third aspect of the present invention.
The decoupling capacitor can be mounted on the intra-package wiring substrate, thereby simplifying the structure for supporting the decoupling capacitor in the encapsulating material. The decoupling capacitor is preferably disposed at the location of the intra-package wiring substrate where the decoupling capacitor is easily connected to the power line of the intra-package wiring substrate.
According to the semiconductor integrated circuit device of a fifth aspect of the present invention, the portion of the encapsulating material for inserting the power lead is connected to the power supply bonding pad of the die through a bonding wire at the die-side end, and the decoupling capacitor is connected to the ground plane and the specified location of the portion for inserting the power lead at either end in the semiconductor integrated circuit device of the third aspect of the present invention.
The frequency of the switching noise current passing through the decoupling capacitor can also be adjusted by the inductance of the power lead. Therefore, by changing the location P1 for inserting the power lead that connects the power-lead-side of the decoupling capacitor, the inductance of the power lead from the connecting location P1 to the end P2 on the side of the printed circuit board for mounting electronic parts is changed, and the frequency of the electromagnetic fields can be adjusted within a desired range to prevent EMI very effectively.
According to the semiconductor integrated circuit device of a sixth aspect of the present invention, the specified location of the portion for inserting the power lead to which the decoupling capacitor is connected is the die-side end of the portion for inserting the power lead in the semiconductor integrated circuit device of the fifth aspect of the present invention.
The inductance from the location P1 of the portion for inserting the power lead for connecting the power-lead-side end of the decoupling capacitor to the location P2 of the power lead of the side of the printed circuit board for mounting electronic parts increases with increase in the length between P1 and P2. On the other hand, the higher the inductance between P1 and P2, the more difficult the current caused by the switching noise of the power circuit of the die to leak to the printed circuit board for mounting electronic parts through the power lead. Therefore, by establishing P1 at the die-side end of the portion for inserting the power lead, the inductance between P1 and P2 can be increased, and the switching noise current of the power circuit of the die is effectively prevented from leaking to the printed circuit board for mounting electronic parts through the power lead.
According to the semiconductor integrated circuit device of a seventh aspect of the present invention, the ground plane is connected to the die-side end of the portion for inserting the power lead into the encapsulating material in the semiconductor integrated circuit device of the fifth or sixth aspect of the present invention.
The inductance from the location P3 of the portion for inserting the ground lead for connecting the ground-lead-side end of the decoupling capacitor to the location P4 of the ground lead of the side of the printed circuit board for mounting electronic parts increases with increase in the length between P3 and P4. On the other hand, the higher the inductance between P3 and P4, the more difficult the switching noise current of the power circuit of the die to leak to the printed circuit board for mounting electronic parts through the power lead. Therefore, by establishing P3 at the die-side end of the portion for inserting the ground lead, the inductance between P3 and P4 can be increased, and the current caused by the switching noise of the power circuit of the die is effectively prevented from leaking to the printed circuit board for mounting electronic parts through the power lead.
According to the semiconductor integrated circuit device of an eighth aspect of the present invention, a layer of a material having a smaller dielectric constant than the dielectric constant of the encapsulating material is provided between the die or the intra-package wiring substrate and the ground plane in the semiconductor integrated circuit device of the first through seventh aspects of the present invention.
The material having a smaller dielectric constant than the dielectric constant of the encapsulating material is, for example, air. If the ground plane is disposed in the vicinity of the die or the intra-package wiring substrate, the capacitance between the signal line of the die or the intra-package wiring substrate and the ground plane will increase to degrade the quality of the signals. By disposing a layer having a small dielectric constant, such as a layer of air, between the die or the intra-package wiring substrate and the ground plane, the capacitance between the signal line of the die or the intra-package wiring substrate and the ground plane can be lowered.
The methods for adjusting the capacitance between the signal line of the die or the intra-package wiring substrate and the ground plane include disposing a layer having a small dielectric constant, as well as establishing the form of the ground plane to a specified curved surface, or providing one or more non-conducting portions partially on the ground plane.
The electric circuit device according to a ninth aspect of the present invention comprises,
a semiconductor integrated circuit device according to any of first through eighth aspects of the present invention,
a printed circuit board for mounting electronic parts whereon the semiconductor integrated circuit device is mounted, and
an external decoupling capacitor provided on the printed circuit board for mounting electronic parts so as to be electrically connected in parallel with the decoupling capacitor of the semiconductor integrated circuit device.
The capacitance of the external decoupling capacitor is typically equal to the capacitance of the decoupling capacitor in the semiconductor integrated circuit device. However, the frequency range of EMI that can be prevented for the entire electric circuit device can be expanded by adequately differentiating the capacitance of the external decoupling capacitor from the capacitance of the decoupling capacitor in the semiconductor integrated circuit device.
Electronic equipment or control equipment according to a tenth aspect of the present invention comprises the semiconductor integrated circuit devices according to the first through eighth aspects of the present invention.
The electronic equipment includes computers, audio equipment, and communications equipment; the control equipment includes, for example, control devices equipped in motor vehicles or industrial machinery and equipment. The semiconductor integrated circuit device according to the present invention can not only be used in electronic equipment such as computers, audio equipment, and communications equipment, but also be incorporated in any equipment that requires countermeasures against EMI, such as the control devices for motor vehicles and industrial machinery and equipment.